The present invention relates to a molecular vacuum pump, which has a stator, a rotor, and a housing, and in which, during operation, a narrow gap is maintained between the stator and the rotor. The pumping characteristics of such pumps depend significantly on the size of the gap between the rotor and the stator.
Molecular vacuum pumps are typically constructed using an elastic connection between the stator and the rotor to prevent transfer of vibrations between the stator and the rotor. The shaft bearings are typically supported by elastomer rings in the housing. For example, German publication DE-U-80 27 697 discloses a rotor equipped with a spindle bearing, and completely supporting the rotor/spindle assembly in the housing by O-rings.
The stator/rotor gap of prior art molecular vacuum pumps did not fall below a few tenths of a millimeter, because this is the minimum tolerance practically obtainable using the elastomer coupling of the prior art.
The present invention contemplates a new molecular pump design which accommodates tighter stator/rotor gaps than is possible by the prior art methods.
According to one aspect of the invention, a stator and a rotor are technically coupled, relative to vibration, and the coupled stator and rotor are jointly fastened in a housing via vibration elements. xe2x80x9cTechnically coupled, relative to vibrationxe2x80x9d shall mean that the rotor unit and the stator unit undergo essentially identical vibrations, so that significantly smaller gaps are practical between the stator and the rotor components than has been achieved by prior art designs. The joint vibrations of the coupled stator and rotor are absorbed by the vibration elements, by means of which the coupled stator and rotor are supported in the housing.
Preferably, the coupling between the rotor and the stator is a rigid coupling, whereby the size of the gap between the rotor and the stator is limited solely by the tolerances of the extruded and machine-produced components. These tolerances are sufficiently low that substantially lower gap tolerances are obtainable versus prior art designs which utilized elastomers.
For reasons of functional efficiency, it is frequently not possible to realize a rigid coupling. In such instances, there are preferably one or more vibration elements arranged between the stator unit and the rotor unit, whereby relative vibrational movements therebetween are permitted. The maximum amplitude of such vibrational movements is, however, substantially reduced compared with prior art designs, because the determinative joint vibrational movements of the stator and the rotor are absorbed by the vibration elements supporting the stator and rotor combination in the housing. A drastic reduction in the gap between the stator and the rotor components versus the prior art designs is therefore still achieved.
For example, the O-rings between the stator and the rotor units can be significantly more rigid than the outer vibration elements. Taking into consideration the respective vibrating masses, a vibrational amplitude ratio of 20:80 is achieved thereby.
Other advantages of the invention will be evident to those of ordinary skill in the art from the examples described in the following detailed description and the attached drawings.